Method of constructing a thin-walled cannula

ABSTRACT

THE INVENTION DISCLOSED HEREIN PERTAINS TO THE MATERIALS OF AND METHODS FOR CONSTRUCTING THIN-WALLED CANNULAS FOR USE IN THE BODY OR IN CLOSE PROXIMITY THERETO FOR TRANSPORTING FLUIDS.

Aug- 15, 1972 H. H. J. ZWART 3,684,605

METHOD OF CONSTRUCTING A THIN-WALLED CANNULA Filed Jan. 21, 1970 INVENTOR. HANS H. J, ZWART AGENT United States Patent O 3,684,605 METHOD F CONSTRUCTING A THlN-WALLED CANNULA Hans H. J. Zwart, Salt Lake City, Utah, assigner to The University of Utah Filed Jan. 21, 1970, Ser. No. 4,668 Int. Cl. B65h 81/00 U.S. Cl. 156-175 3 Claims ABSTRACT OF THE DISCLOSURE The invention disclosed herein pertains to the materials of and methods for constructing thin-walled cannulas for use in the body or in close proximity thereto for transporting luids.

Cannulas for use in the body are generally restricted in outside diameter by the size of the opening or lumen through which they must pass. As a result, the internal dimensions of the cannula are restricted by the wall thickness of the cannula. To permit maximum ow of fluid through the cannula it is mandatory that the wall thickness be reduced to the fullest extent possible while at the same time providing sullicient rigidity within the walls to prevent their collapse under the expected operating conditions.

One use for a thin-walled cannula is as an endotracheal tube in infants where size of the resulting air passageway is of crucial importance particularly during the exhalation phase of breathing since this phase of breathing cannot be assisted mechanically.

Another application is in heart assist devices that bypass a portion of a diseased heart thus reducing its work load and restoring the deteriorated blood circulation. This greatly improves the hearts chances of healing so that it may again resume its normal blood supplying function. Such a bypass operation has been described by Dr. Hans Henk Jan Zwart in Complete Left Heart Bypass With Thoracotomy, S.O.L. Otfsctdruk. Amsterdam, 1966. The bypass is accomplished by inserting a cannula into the left pumping chamber of the heart by passing the cannula through an artery to thereby divert a portion or all of the blood which llows to that part of the heart. The blood is then passed through an auxiliary pumping means located externally of the body and thereafter returned to the arterial system of the body at an increased pressure thus temporarily relieving the heart of this pumping burden.

Passage of the cannula into the heart is accomplished by inserting the cannula through a blood vessel from a point near the surface of the body thus obviating the need for an open chest operation.

Research in the iield of blood transport systems has shown the need for a thin-walled cannula which can be inserted into the lumen of the blood vessel to thereby di vert substantially the total How of blood from the blood vessel into the cannula. Since blood ow is very sensitive to the internal dimensions of the transport cannula and the external diameter of the cannula is fixed by the interna] dimensions of the blood vessel through which the cannula is passed, it is mandatory that the Wall thickness of the cannula be reduced as much as possible to permit maximum blood ow while at the same time retaining suilicient rigidity within the walls of the cannula to prevent collapse of the cannula during periods of negative pressure. At the same time, the cannula must be ilexible along its length to be readily adaptable to the contour of the blood vessel and reduce tissue damage to a minimum.

In circumstances where the external diameter of the cannula is not greatly restricted such a use as a wound drain, it is still preferable to use a thin-walled cannula 3,684,605 Patented Aug. 15, 1972 Mice since this reduces the dimensions of the wound that must heal after the cannula has been removed. Reduction of wound dimensions also means a corresponding reduction of the potential pathway for infectious organism.

It is an object of this invention to provide an improved cannula for the transportation of lluid substances wherein the cannula has a maximal inside diameter per outside diameter.

It is another object of this invention to provide a thinwalled cannula wherein the walls are rigid enough to withstand an internal negative pressure of at least 200 mm. Hg.

It is still a further object of this invention to provide a thin-walled cannula wherein the materials of construction are compatible with and non-injurious to living tissue.

A still further object of this invention is to provide a material of construction which has relatively good adhesion characteristics in contact with glass bers.

It is another object of this invention to provide a cannula with improved flexibility along its length.

It is another object to provide a cannula for by-passing the human heart and wherein the necessity for opening the chest cavity is eliminated.

These and other objects will become more fully apparent when viewed in conjunction with the following drawing and description.

The drawing shows a partial cutaway view of a cannula under construction as it is formed about a mandrel.

Referring to the drawing, the cannula is shown generally at 10 and comprises one or more layers of polymeric material 11 over which glass fibers 12 are wound and subsequently covered with one or more layers of the polymeric material as indicated at 13. A multiplicity of layers of glass fiber and polymeric material may be used to develop the desired thickness and strength of the cannula wall. In addition, the ilexibilty of the cannula may be suitably altered along its length by the appropriate control of the layers of polymeric material and winding techniques of the glass fibers. As illustrated in the drawing, the glass fibers 12 are shown spirally wound with each successive spiral lying in a plane substantially perpendicular to the axis of the mandrel although any suitable technique could easily be substituted for the one illustrated since glass liber winding techniques are well known in the art. In the presenty preferred embodiment glass bers have been used although other ilexible fibers could be used.

In the presently preferred embodiment, the polymeric coating is comprised of a mixture of polyurethane (commercially available as B. F. Goodrich #5701 F1 Estane), a rigid polyester (commercially available as United States Manufacturing Company Polyester Resin #4110), and a exible polyester (commercially available as United States Manufacturing Company Polyester Resin #4135). The steps of manufacture of the polymeric coating comprise dissolving the polyurethane in a solvent such as tetrahydrofuran on the basis of about 20 percent by weight polyurethane to tetrahydrofuran. The polyesters are added to this mixture on the order of about 1 part rigid polyester (#4110) and 3 parts ilexible polyester (#4135) to 96 parts of the polyurethane and solvent mixture. Catalyzing agents in suitable quantities are then added to the resulting mixture. These catalyzng agents comprise benzoyl peroxide and a promoter (commercially available as United States Manufacturing Company Naugatuck Promoter #3).

The mandrel for the cannula is comprised of a rigid member 14 encased in a section of elastic tubing 15 and secured to the distal end of the tubing. The elastic tubing 15 serves to establish the internal dimensions of the cannula. If the external diameter of the elastic tubing 15 in its undeformed state is the desired internal diameter of the cannula, the cannula is then formed about the mandrel; otherwise, the elastic tubing is either stretched or inflated and secured by securing member 17 to provide the desired diameter for the internal diameter of the cannula. If necessary, air is forced between the elastic tubing 15 and the rigid member 14 as indicated by air space 16 to facilitate the insertion or removal of the rigid member 14 from the elastic tubing 15 when a snug lit between the two members is desired.

In the presently preferred embodiment, the elastic tubing is comprised of a silicone rubber, for example, silicone rubber commercially available as Dow Corning Silastic and is coated with a release agent (Silastic RTV mold release, not shown) which prevents the adhesion of the polymeric material 11 to the elastic tubing 15.

As an alternate method of construction of the mandrel, a dissolvable coating 15 is formed about the rigid member 14 in place of the elastic tubing. After the cannula has been formed about the mandrel, the mandrel is withdrawn by dissolving the dissolvable material with a suitable solvent.

Layers of polymeric material are applied to the mandrel by any suitable means such as spraying or dipping and the glass ber is wound about the mandrel as previously described either as a single layer or in alternate layers with polymeric material. A final layer or layers of polymeric material are thereafter applied and the polymeric material of the completed cannula is suitably cured.

After suitably curing the polymeric material of the cannula, the mandrel is removed from the lumen of the cannula.

Various adapters which may be required at the ends of the cannula may be easily secured to the cannula by suitably positioning them on the mandrel prior to, during,

or after manufacture of the cannula so that there is a g close bonding between the material of the adapter and the polymeric material of the cannula.

I claim:

1. A method of constructing a cannula of substantially reduced wall thickness to thereby increase the amount t of Huid that can pass through a cannula of a tixed outside diameter and at any given pressure, said method comprising the steps of:

(a) enveloping a rigid member with an elastic tubing to form a mandrel and thereafter securing one end of said elastic tubing to said rigid member;

(b) stretching said elastic tubing to achieve the desired outside diameter of said elastic tubing;

(c) securing the free end of said stretched elastic tubing t0 said rigid member;

(d) coating the mandrel thus formed with a releasing compound;

(e) covering said mandrel with one or more layers of a polymeric material over which a glass fiber is suitably wound either singly or in combination with a polymeric material;

(f) covering the final glass fiber layer with one or more layers of polymeric material;

(g) suitably curing the polymeric material of the cannula; and

(h) separating the cannula from the mandrel.

2. A method of constructing a cannula of substantially reduced wall thickness as detined in claim 1 wherein the material of construction is a polymeric material mixture comprising a polyurethane, a rigid polyester, and a ilexible polyester, said materials comprising a ratio of approximately 96 parts polyurethane dissolved in an evaporative solvent on the order of approximately 20 percent by weight polyurethane to solvent, said polyesters comprising approximately 1 part rigid polyester and approximately 3 parts flexible polyester.

3. A method of constructing a cannula of substantially reduced wall thickness as dened in claim 1 wherein said elastic tubing is comprised of a silicone rubber.

References Cited UNITED STATES PATENTS 3,425,982 2/1969 Fink 156-173 3,509,883 5/1970 Dibelius 12S-348 3,498,286 3/1970 Polanyi et al. 128--348 3,485,234 12/1969 Stevens 128-348 3,416,531 12/1968 Edwards 12S-348 OTHER REFERENCES Reynolds et al., Surgery, December 1965, vol. 58, No. 6, pp. 938-40.

CARL D. QUARFORTH, Primary Examiner E. E. LEHMANN, Assistant Examiner U.S. Cl. X.R. 

